MEMS combine micro-scaled mechanical and electrical components into integrated systems. MEMS are typically used as microsensors, microactuators, and the like, and have found beneficial use for implementing accelerometers and other such inertial instruments. MEMS may also be used in chemical detectors, pressure sensors, thermal and/or electrostatic actuators, and the like. The use and applicability of such devices is only increasing as the intelligence and complexity of the MEMS increases, at the same time that the overall scale of the devices is decreasing into the nano-scaled, nanoelectromechanical systems (NEMS).
Many sub-millimeter MEMS/NEMS utilize capacitive connections or operations to implement the sensing or actuating functions. Moreover, many MEMS/NEMS use thermal energy for operation, which may require running electrical current across such MEMS/NEMS elements. The electronic circuitry for all types of these devices continues to increase. Therefore, in order to maintain the functionality of the capacitive elements, thermal elements, and the overall growing embedded electronics, it is desirable to create MEMS/NEMS devices with electrical isolation properties. With the bulk of current technology settled mostly into the sub-millimeter MEMS region, techniques have been developed for fabricating micro-scaled devices with electrical isolation elements.
One such method, disclosed in U.S. Pat. No. 6,291,875, issued to Clark et al., entails etching a trench to physically separate the conductive material on the device and then filling that trench with an insulating material in order to re-attach the two portions. Thus, the electrical isolation is generally created by cutting the conductive connection and then mending the cut with an electrically isolating substance. With the insulating layer added, the device is again mechanically connected allowing the micromechanical aspect of the MEMS device to continue.
One problem associated with the trench-fill method for electrically isolating MEMS devices, are the cavities or voids that are typically formed in the insulating material filling the trench. The material used for the insulating layer typically does not uniformly fill the trenches. The unevenness may generally cause the upper portion of the trench to close before the lower portion of the trench is completely filled. This creates gaps or voids within the trench that can sometimes weaken the structural integrity of the device and can lessen the thermal conductivity, which is essential for reliable operation of some devices, such as thermal actuators.
The Clark, et al., patent discusses this problem and is directed to a method for improving the trench-fill by adding condyles to the trenches. Condyles are generally openings or “knuckles” at the trench ends that are typically wider than the basic trench width to allow the insulating material to more easily fill the trench more before closing off. Thus, the Clark patent requires etching trench patterns to attempt to alleviate the problems caused by the voids or cavities typically formed in regularly shaped trench-fills.
The addition of the condyles in the Clark patent does not guarantee that voids or cavities will not form. The increased opening areas likely improve the fill of the insulating material, but because of the non-uniformity and lack of precise control over the fill process, voids or cavities could still form for the same reasons. Therefore, while Clark describes an improvement to the trench-fill isolation methods, it does not guarantee success.
Outside of the electrical isolation techniques, mechanical connectors have been fabricated by etching male and female connection ends onto MEMS devices that are intended to connect. In such mechanical elements, the first MEMS device is etched with the female/receptacle end, and the second MEMS device is etched with the male/protruding end. As the two ends are inserted together, flanges or extruding portions of the male part deflect and then rebound when fully inserted. Thus, the two parts are frictionally maintained connected. These technologies have not been used with electrical isolation and would likely not be available for accepting dielectric materials or other non-conducting materials within the connection region.